Kilns are essential to the manufacture of ceramics, which, by definition, require high temperature treatment. During the firing stage, chemical and physical reactions occur that permanently alter the material. Proper firing of clay converts the relatively weak and malleable substrate into a rigid and strong structure. The final material characteristics of articles of ceramic are determined by a number of factors, including the preparation and composition of the clay substrate, the temperature at which it is fired, and any glazing that might be applied thereto.
One type of kiln often used by finished ware manufactures to fire ceramic products is commonly referred to as a hobby kiln, which can be used for firing, curing, and heat treating. Kiln styles include the chamber raise kiln, the top loading kiln, and the front loading kiln. The chamber raise kiln is often referred to as a top hat kiln since an upper body portion with sides, a top, and an open bottom is raised and lowered by a winch system relative to a support surface for enabling the insertion, heat treatment, and removal of articles. A front loading kiln typically comprises a box shape with a vertically hinged front door.
Top loading kilns are perhaps the most common type of hobby kiln. A typical top loading kiln is indicated generally at 10 in FIG. 1. The top loading kiln 10 has a body portion formed by a fixed peripheral sidewall 12 and a bottom 25. The sidewall 12 and the bottom 25 together define a firing chamber 16 for receiving articles to be heat treated. A lid 14 with a handle 32 is coupled to the sidewall 12 by a hinge arrangement 18. The lid 14 can be retained in an open disposition by a support bar 22 or other means. When closed, the lid 14 seals off the chamber 16 to enable proper heating of the kiln 10.
The sidewalls 12 of top loading kilns 10 can be of a variety of shapes, including round as in FIG. 4, square, oval, or faceted, such as by having from five to twenty or even more facets. For example, the kiln 10 in FIG. 1 is faceted with ten sides while the kiln 10 in FIG. 3 is faceted with eight sides. The thickness T of the sidewalls 12 can vary, but is commonly 2 and ½ to 3 and ½ or more inches. Similarly, the effective inner diameter D of kilns 10 varies depending on, among other things, the needs and budget of the artisan and the design of the manufacturer.
Electric heating elements 20, often made from resistance wire, are disposed in grooves 21 on the interior surfaces of the sidewalls 12. The kiln 10 receives power through a power cord 30. Other kilns 10 are gas fired. A control box 24 with a control panel 28 enables control over the operation of the kiln 10, and a plurality of venting louvers 26 enables heat to be dissipated from the control box 24. The sidewall 12, lid 14, and bottom 25 of the kiln 10 are typically formed by blocks of firebrick, which can be dry fit or cemented together. The firebrick can be enveloped in a metal lining.
Firebrick is a refractory ceramic material built primarily to withstand high heat and to demonstrate low thermal conductivity, which saves energy and facilitates sustained high internal operating temperatures. In that regard, it will be noted that kilns 10 are fired not just to a temperature, but to what are typically referred to as cone levels, which account for time and temperature. The firebrick used in electric and gas-fired kilns 10 is often relatively porous thereby rendering the brick lighter, easier to form, and better thermal insulators than denser brick.
The sidewall 12 of the top loading kiln 10 has an upper peripheral surface 15 that is flat and horizontal for providing a good seal relative to the lower surface of the lid 14. A tight seal is important for a number of reasons, including for energy efficiency and to enable the kiln 10 to reach desired cone levels. Furthermore, a good seal will help prevent caustic fumes from escaping from the firing chamber 16 and causing adverse effects on bystanders and surrounding components of the kiln 10. Furthermore, certain kilns 10 rely on a tight seal to permit a negative pressure to be created by a downdraft vent system that, when installed and operational, limits the emission of fumes by evacuating them from the chamber 16 and exhausting them.
Unfortunately, while advantageous for its thermal and other properties, firebrick is very fragile. As such, the soft brick is vulnerable to chipping, breaking, and general wear. For example, as artisans repeatedly lean against the sidewalls 12 to reach into the firing chamber 16, the firebrick at the upper peripheral edge surface 15 is often worn down over time and otherwise damaged. Furthermore, articles, such as ceramic structures and kiln furniture, can accidentally strike and damage the upper edge surfaces 15 of the sidewalls 12 while being inserted and removed. Further risk of damage and wear comes from the habit of some practitioners of propping the lid 14 of their kiln 10 open by placing a brick or other obstruction between the lid 14 and the upper edge surface 15 of the sidewall 12.
Over time, therefore, a wearing away of the upper peripheral edge surface 15 leads to chips 36 and damaged edge portions 34. The integrity of the seal between the lid 14 and the upper peripheral edge surface 15 can be compromised, particularly where the damage extends entirely from the inner edge to the outer edge of the upper peripheral edge surface 15, thereby leading to reduced performance and potential harm to surrounding persons and structures. While repair of the damaged peripheral edge surface 15 is possible, it is expensive and inevitably decreases the life and value of the kiln 10.
With an awareness of the problems and dangers deriving from such damage to the upper peripheral edge surfaces 15 of kilns 10, it has been appreciated by the present inventor that a structure and method for protecting a kiln 10 during loading and unloading would represent a useful advance in the art.